A calendar date display mechanism is shown in FIG. 1 accompanying the present patent application. Indicated as a whole by the general reference numeral 1, this calendar date display mechanism is driven by an intermediate wheel 2 which is fixed to an hour wheel (not shown). In other words, the intermediate wheel 2 turns in a clockwise direction and completes a full turn in twelve hours. This intermediate wheel 2 engages with a calendar date drive wheel 4 which turns in an anti-clockwise direction at a rate of one turn in twenty-four hours. This calendar date drive wheel 4 has a finger 6 with which it drives, at a rate of one tooth pitch per day, a calendar date wheel 8 which is indexed by a pawl 10 and carries a cam 12. At one point of its profile, the cam has a steep flank 14 which marks the passage between the calendar date of the last day of a given month and the calendar date of the first day of the following month, in other words between the calendar date “31” and the calendar date “1”.
The calendar date display mechanism 1 is completed by a control lever 16 having at one of its ends an arm 18 whereby it rests against the cam 12 during a period of normal operation, and having at its other end a rack 20 whereby it engages with a calendar date display wheel 22 which carries the calendar date indicator (not shown). The control lever 16 is pivoted at 24 whereas a second lever 26 called the return lever is pivoted at 28. This return lever 26 has a structure similar to that of the control lever 16, in particular comprising a rack 30 whereby it engages with the calendar date display wheel 22. As shown in FIG. 1, the return lever 26 is constrained by a spring element 32 which tends to turn it in a clockwise direction. In turn, the return lever 26 tends to turn the calendar date display wheel 22 in an anti-clockwise direction, which tends to turn the control lever 16 in a clockwise direction and to keep its arm 18 resting against the profile of the cam 12.
At the end opposite to the one that carries the rack 30, the return lever 26 has a feeler 36 which cooperates with a circular cam 38, centred on the centre of the movement, on the inner profile of which the feeler 36 of the return lever 26 comes to rest. Note that in the state in which the calendar date display mechanism is shown in FIG. 1, the feeler 36 of the return lever 26 is located at a step 40 that the circular cam 38 has on its inner profile.
FIG. 1 shows that the arm 18 of the control lever 16 is at the bottom of the steep flank 14 that the cam 12 has on its profile. This means that the calendar date indicator mechanism, to which in particular the calendar date wheel 6 and its associated cam 12 belong, has just passed from the last calendar date “31” of a given month to the first calendar date “1” of the following month. Let us now suppose that, starting from this situation, the indication of the calendar date must be corrected. If, during this correction, the calendar date wheel 8 turns in a clockwise direction, no particular problem is observed. The arm 18 of the control lever 16 will follow the profile of the cam 12 and drive, by its rack 20, the calendar date display wheel 22, which will have the effect of increasing step by step the indication of calendar date. By contrast, it is a different matter if the calendar date correction operation causes the calendar date wheel 8, and thus the cam 12, to rotate in the opposite direction. In fact, in this case, the arm 18 of the control lever 16 will brace against the steep flank 14 of the profile of said cam 12 and the mechanism will be blocked. This is why an arrangement must be made so that, when a backward correction is made to the indication of the calendar date, the arm 18 of the control lever 16 is moved aside from the path of the cam 12. The circular cam 38, connected to a winding stem 42, is provided to resolve this problem.
In fact, the winding stem 42 is connected cinematically to the circular cam 38 via an element 44 which makes it possible to transform a linear movement of said winding stem 42 into a pivoting movement of said circular cam 38. Supposing that the winding stem 42 is pulled out in order to move it from its neutral winding position to a first pulled position, this causes the annular cam 38 to pivot in an anti-clockwise direction in a way that will not be described in further detail here. Nevertheless, it will be understood that the pivoting of the annular cam 38 in an anti-clockwise direction allows the arm 18 of the control lever 16 to be distanced from the path of the cam 12. Indeed, under the pivoting effect of said annular cam 38, the feeler 36 of the return lever 26 moves up along the flank 46 of the step 40 and slides along the inner perimeter of the annular cam 38. In doing this, the return lever 26 pivots in an anti-clockwise direction and causes, via the calendar date display wheel 22, the pivoting of the control lever 16, also in an anti-clockwise direction, which has the effect of distancing the arm 18 of this control lever 16 from the path of the cam 12.
Moving the winding stem 42 from its first pulled position to a second pulled position causes an additional pivoting of the annular cam 38. This pivoting, however, has no effect on the return lever 26 since its feeler 36 has climbed the flank 46 of the step 40 and slides on the inner perimeter of the annular cam 38. The arm 18 of the control lever 16 therefore remains beyond the path of the cam 12.
Let us now discuss the reasons why it is necessary to move aside the arm 18 of the control lever 16 from the path of the cam 12. Supposing that the winding stem 42 is brought into its first pulled position, it can be turned forwards or backwards. Now, when the winding stem 42 is turned, the hour wheel (not shown), and therefore also the intermediate wheel 2, are turned. If the intermediate wheel 2 turns in a clockwise direction, in other words the direction in which it turns during normal operation, the cam 12 turns in an anti-clockwise direction and the arm 18 of the control lever 16 slides without any problem along the profile of said cam 12. By contrast, if the intermediate wheel 2 turns in an anti-clockwise direction, the cam 12 will turn in a clockwise direction and the arm 18 of the control arm 16 will brace against the steep flank 14 of said cam 12 and jam. This is why, in this case, the arm 18 of the control lever 16 must be moved aside from the path of the cam 12.
The calendar date display mechanism 1 described above is particularly well suited for use in a time zone type watch. In the case of a time zone watch of this type, the winding stem 42 has three set positions, namely a neutral position in which it allows the clockwork to be wound, a first pulled position which allows the time zone indication to be corrected (it may be a jumping indicator which goes forwards or backwards a whole step of one hour without the minutes display being affected) and a second pulled position which allows the watch time to be set. It must therefore be possible for the calendar date drive wheel 4 to drive, via its finger 6, the calendar date wheel 8 in both a clockwise and an anti-clockwise direction. This is done without any difficulty when the correction is made by means of the winding stem 42. Indeed, in this case, the winding stem 42 drives the hours wheel and thus the intermediate wheel 2 which in its turn drives the calendar date drive wheel 4 and its finger 6. By contrast, a problem may arise when one wishes to correct the indication of a calendar date by means of the rapid corrector 48 shown in FIG. 1. Indeed, by repeatedly pressing the rapid corrector 48, the indication of the calendar date can be increased by steps of one unit, making this indication pass for example from “1” to “2”, then from “2” to “3” and so forth. It must be understood that, in this scenario, the hour wheel, the intermediate wheel 2 and therefore the calendar date drive wheel 4 are substantially stationary. Consequently, if a rapid adjustment of the indication of the calendar date is desired while the finger 6 is engaged in the toothing of the calendar date wheel 8 (for a duration of approximately 1 to 1 and a half hours around midnight when the drive of the calendar date wheel 8 by the calendar date drive wheel 4 is of the trailing type), the mechanism will be jammed. There is thus a need for a drive system, for example, in a calendar date display mechanism, and more generally for any type of device that displays a time-dependent value, which system is capable of driving such a mechanism or device both in a clockwise and in an anti-clockwise direction under normal operating conditions and is capable of being moved aside during the rapid correction phase.
In order to meet this need, different solutions are already available. For example, a rapid adjustment mechanism for a calendar watch is known through Patent FR 2.080.602 in the name of the Hamilton Watch Company. As shown in FIGS. 1 and 2 of the corresponding description on page 6, line 35 to page 7, line 38, the rapid adjustment action of the calendar date ring is performed by means of a ratchet articulated on a first pivot and a ratchet spring articulated on a second pivot. A shoulder of the ratchet is normally abutted against the part where the spring is fitted to the second pivot. During the rapid correction phase of the calendar date ring, the ratchet pivots in an anti-clockwise direction around the first pivot within the peripheral limits of the teeth of the calendar date ring. Each rotation of the ratchet advances the calendar date ring one by one tooth. When the watch display is corrected in the opposite direction, the ratchet is driven in a clockwise direction, which makes it pivot about the first pivot against the action of the spring when it encounters a tooth of the calendar date ring. This pivoting effect makes the ratchet pass onto the teeth of the calendar date ring without driving the latter backwards.
The above-described Hamilton system is a ratchet system which drives the calendar date ring in a clockwise direction only and is moved aside when said ring is corrected in the opposite direction. Said ratchet is not capable of driving the calendar date ring in both a clockwise and anti-clockwise direction during the normal correction phase of the calendar date display.
A rapid reset ratchet calendar date mechanism is also known through Patent FR 1.426.305 in the name of Horlogerie de Savoie. As emerges from FIGS. 1 and 2 and the description from page 1, right-hand column, line 19 to page 2, left-hand column, line 6, the rapid reset mode operates via a ratchet which is driven in an anti-clockwise direction and which, under the action of a spring, is held against a pin. After sufficient rotation, the end of the ratchet abuts against the face of the tooth of the calendar date ring, which forces the ratchet to release itself from the pin, its end jumping over the tooth against the toothing then penetrating into the next gap in this toothing.
The ratchet system briefly described above is capable of driving the calendar date ring in one direction only. In the opposite direction, it is moved aside in the rapid correction phase.
A watch with a calendar date mechanism is also known through U.S. Pat. No. 3,992,868 in the name of the Citizen Watch Co. Ltd. As emerges from FIG. 4 and the corresponding description in column 2, lines 3 to 53, a resilient lever comprising a drive ratchet and two resilient arms is mounted in a pivoting manner on the calendar date wheel and held in place by a rivet. Under normal conditions, the resilient spring is positioned so that the arms surround a hub of the calendar date wheel. When the ratchet is subjected to a drive force in a first direction, one of its arms is elastically deformed and, when the force exceeds a set threshold, this arm is further deformed and comes into contact with a switch pin. On the other hand, when the ratchet is forced in a second direction opposite to the first during a rapid rotation of the calendar date plate, the other arm is deformed. The ratchet of the resilient lever acts so as to drive the calendar date plate in rotation, then the ratchet comes into contact with the switch pin due to the deformation of the arm.
Neither does the above-described Citizen system enable the calendar date plate to be driven in both directions.